Is it necessary for a Buddhist to believe that existence is suffering?

It appears that Buddhism depends on a central premise -- that all worldly existence = suffering / dukkha. Are there Buddhist teachers or traditions that teach a joyous approach to worldly life? Are there any teachings that profess existence is a joyous, if sometimes painful experience, or at least a tolerably pleasant experience? An eternal roller-coaster ride of birth-and-death, joy and sorrow, that one need not seek to escape?